Submarine signal system



Aug 6, 1946- w. P. MASON SUBMARINE SIGNAL SYSTEM Filed 001'.. 14, 1942 2 Sheets-Sheet 1 4 VVE/WOR BVI/14 P. MASON from/Ev Aug, L6, 1946. w, P, MASON A 2,405,225

SUBMARINE S IGNAL SYSTEM Filed oct. 14, 1942 2 Sheets-sheet 2 F/G.6 Y

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l 0 l0 20 a) 40 50 FREQUENCY/N K/L OCYCLES PER SECOND Y 'ao- I I l l I l -l I o lo 2o so 4o Y so so 1o so FREQUENCY /N k/LocycLEs PER seco/vo /N/E N TOR BV W P. MASON Patented Aug. 6, 1946 SUBMARINE SIGNAL SYSTEM Warren P. Mason, West Orange, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application October 14, 1942, Serial No. 462,042

' 6 Claims. (Cl. 177-386) This invention relates to submarine signaling Y systems and more particularly to submarine signal projectors.

An object of this invention is to radiate or project signal waves of a wide range of frequencies into and under Water.

Another object of the invention is to convert electrical signals into sonic or supersonic signals in Water with substantially constant efficiency over a broad band of frequencies.

In accordance with the invention, the radiator or projector comprises piezoelectric crystal means, for example, electrically connected units or blocks of Rochelle salt crystals which may be of the l-degree Y-cut type. The resonant frequency of the crystal means is preferably well beyond the upper limiting frequency of the frequency band of interest. Resistance means is connected in series with the crystal means and is chosen of such impedance as to be substantially equal to the reactive impedance of the crystal means at a relatively low frequency whereby, at the higher frequencies of interest, the current into the crystal means will be controlled by the resistance and be substantially independent of frequency.

A more complete understanding of the invention will be derived from the detailed description that follows, taken in conjunction with the appended drawings, wherein:

. Fig. 1 shows a front elevational view of apparatus embodying the invention;

Fig. 2 shows a side elevational view of the apparatus of Fig. 1;

Fig. 3 shows a front View of the piezoelectric crystal means, projector or radiator included in the apparatus of Fig. 1, partly broken away and partly in section to show details of structure, and Fig. 3A an enlarged elevational view of one of the component crystal blocks of that means showing the electrical wiring connections between the individual crystal plates;

, Fig. 4 shows a sectional view of the crystal means of Figs. 1 and 3 taken along the line 4-4 of Fig. 1;

Figs. 5, 6 and 7 show equivalent electrical circuits or analogues of the piezoelectric crystals in the projector of Figs. l and 3 under different conditions;

Fig. 8 shows curves illustrating the calculated elciency of conversion with respect to frequency, of the arrangement of this invention; and

Fig. 9 shows curves evidencing the responsefrequency characteristic determined from experunental tests of an actual embodiment of the invention. V

Figs. 1 to 3, 3A and 4 illustrate a submarine signalling device or apparatus embodying the invention. It comprises a frame or support IB having an enlarged, hollow, substantially cylindrical portion II, and a bail or carrier portion I2 whereby the device may be submerged or suspended at the end of rope or cable I3 in a body of water. A signal wave projector or radiator I4 is supported from the portion I I by a pair of metallic tubes or pipes I5 through Which electrical connections may be made between components in the hollow portion II and the projector.

The projector is constructed of a plurality of piezoelectric crystal units or blocks I6. Each of these runits may comprise four Ll-degree Y-cut Rochelle salt crystals or plates Il, I8, I9, ZIJ, each of which may be 1.6 centimeter longy 1.0 centimeter .wide and .4 centimeter thick. When connected together they constitute a block or unit 1.6 cm. 1.6 cm., with a width in the radiation direction of 1.0 centimeter. The crystal plates are coated on their faces With platinumrhodium about .00017 inch in thickness. The innermost faces 2|, 22 and the two outermost faces 23,24 are connected together with a copper wire 25 to constitute one terminal of the unit; the intermediately located other two pairs of crystal faces are connected together by a second copper wire 26. The crystal units, which, in a specific embodiment were twenty-five in number, are fastened to and between thin ceramic plates or discs 21, 28. 'Ihe latter may be of the order of .1 centimeter thick. The crystal unitsceramic plates assembly is enclosed by a rectangular frame 29 the open ends of which are closed by a pair of phosphor-bronze diaphragms 3B, 3l of the order of .003 inch in thickness, soldered at their marginal portions to the frame 29 and fastened on their inner surfaces to the ceramic plates 21, 28.

The procedure in assembling the projector may be as follows. "I 'he crystal blocks I6 are connected in parallel by suitable wiring and arranged symmetrically, as shown, between the ceramic plates 2l, 28 to which they may be glued or cemented. The diaphragm 30 is soldered to the frame 29 and the crystal units-ceramic plates assembly fastened thereto by cementing the ceramic plate 2l to the inner surface of diaphragm 3|). By having the frame 29 of suficient size, a small clearance may be provided between the crystal units for their wiring which terminates at the two leads 32, 33, brought out of the frame through the glass seals 34 in the tubes I5; and for dry Rochelle salt 35 to keep the humidity low. The second diaphragm 3l is cemented to the ceramic plate 28, and, after the a pan of water during the final soldering operaf` tion. The cement used is preferably one that has' a very rubbery consistency when dry, and may be of the type known commercially a's Vulcalock.

The portion Il encloses a transformer 31fand a pair of electrical resistances 38, 39,7the latter being connected in series with the parallel-con- CTI nected crystal units and theV secondary winding of the transformer, the portion I I otherwise being oil-filled as shown by the dashed horizontal lines designated l). The primary winding of the transformer 3'1 is connected through the conductors 4D of the cable 4i Witha, source (not shown) of electric waves to be converted by the projector into signal waves in the water. This electric wave source may be in a suitable vessel on the'surface of the Water, or at a shore station. The projector is intended to radiate signal Waves over a broad band of frequencies, for example, Y from about kilocycles per second Vup to'about 60 /4 With these values, the element constants become -Thetransformer I transforms from mechanical impedance units (expressed as a ratio of force in dynes to velocity in centimeters per second) to kilocycles per second, with substantially constant eiciency. The resonant frequency of the crystal means should be substantially higher than'the upper, limiting frequency of the band of interest. The resistances 38,239 are ch'osen so as to present a resistive impedance substantially equal to the reactive impedance of the crystal units at a very *low frequency in the frequency band of interest,

namic measurement of the elastic, electric fand Y piezoelectric constantsofRochelle salt, Physical Review, volume 55, (1939) ,pages 775 to789.' The element values for a-single crystal of `the-45-degree Y-cut type, radiating on both sides, eX- pressed in c. g. s. relectrostatic'Y units, become.

Wh'ere K=1'0.0=dielectric lconstant of l5-degree` Y-cut Rochelle salt.

S22f=9-26 10r12=inverse of Youngs modulus along the length.

p=1.775=density of Rochellesalt.

electrical impedance units. Y

When th'e crystal lis used to drive water' and the radiating surface is 1a half wave-length or greater, the mechanical end of the equivalentlci-r'cuit'will be terminated by the radiationresistancef *Y I *1&2* Y. iu 1 K 2 where In general, Ythetelectrical impedance as measured fromr the electrical terminals of the crystal is of interest. For such a case, the: mechanical elements can beV taken .through the electromechanicaltransformer,'the resulting yelements as `shown`inFig56 being r 'i C1 y farads hms. y

In the specific embodiment Vconstructedinfac-l cordance with the invention, one hundred crystals were included. With dimensions ly=l.'0centiI meter, Zw=l'.6 centimeters, and 11s-:.4 centimeter, the constants for twenty-vegparallel connected blocks of four'crystals .each become The distributed capacity resultingfromY th fz5=6.33 1O4=piezoelectric constant of Rochellel presence'of the diaphragms 30,; 3| is vkept l'owby? the inclusion of the' ceramic plates "21, 28 between,` the crystals and diaphragms.` In 'the particular structure, ,the 'added, capacitance, was about" 5 0v Mf- The resonant frequency for this crystal com'- binatio'n isj over 100 ,kilocycles per second; Hence,

up to about 50 kilocycles per second, the vmass., reactance may be neglected and the equivalent.V

circuit may be represented by Fig. 7., lThere sistances 38, 39 are included .in series.V with 'the crystal Vmeans, ,andV withV the secondary winding of the transformer 31. If the rsistances 'are chosen' to have a resistive'impedance equal tothe reactive impedance of the crystalat a relatively low frequency, at the higher frequencies of in-f' terest the current into the radiator will be' controlled by the resistance and Vwill be independentl of the frequency. The impedance presented by the radiator will be primarily the capacitive reactance ofthe shunt condenser and, hence, substantially all of the input current ilows through such condenser, whereby the voltage thereacross is inversely proportional to the frequency. The current into the radiation resistance is controlled primarily by the series capacitance since this presents a much larger impedance than the resistive impedance. Consequently, the current into the radiation resistance will be independent of frequency.

In using the described device to produce a definite pressure, account should be taken of the fact that the radiating surface becomes more directive the higher theV frequencyV because the radiator becomes a larger number of wave-lengths at the higher frequencies. It can be shown that the increased directivity results in an increase in pressure equal to 6 decibels per octave for all frequencies of interest.

With the equivalent circuit of Fig. 7, the eniciency of conversion from electrical to mechanical energy can be readily calculated. 'I'he series resistance (RA) added by the resistances 38, 39 was taken as 80,000 ohms. In the particular case, the transformer 31 transformed from 115 ohms to 75,000 ohms but its loss was less than .5 decibel from to 100 kilocycles per second. From a 75,000-ohm source (Rs) the current in into the radiation impedance is given by Hence the efliciency of conversion is given by the ratio,

2i/RSRR' 6 octave. The Vdivergence of curves D and Eis a measure of the variation in the conversion efliciency of the projector with frequency. It will be observed that between l0 and 60 kilocycles per second, the variation is of the order of only two decibels.

Although this vinvention has been disclosed with reference to a specic embodiment, it Will be understood that it is not limited thereto but is of a scope evidenced by the appended claims.

What is claimed is:

1. .A submarine signal projector for signal radiation over a broad band of frequencies with substantially constant conversion eiiiciency, comprising a plurality of -degree Y-cut Rochelle salt crystals connected in parallel, and electrical resistance meansnconnected in series with Vsaid crystals and having a resistive impedance substantially equal to the reactive impedance of the crystals at a relatively low frequency in the band.

2. Submarine signaling means comprising a plurality of Ll-degree Y-cut Rochelle salt crystals connected in parallel, and electrical resistance means connected in series with said crystals and of a resistive impedance substantially equal to the reactive impedance of the crystals at a relatively low frequency in the band of frequencies below the resonant frequency of the crystals.

3. Submarine signaling means comprising a plurality of Ll5-degree Y-cut crystals for translating electric energy into signal waves in water over a band of frequencies the upper limiting frequency of which is substantially lower than the resonant frequency of the crystals, and electrical resistance means in series with said crystals and of a resistive impedance substantially equal to the reactive impedance of the crystals at a relatively low frequency in said band.

4. A device for converting electrical energy into acoustic energy for radiation to a water medium with substantially constant eiciency over a wide band of frequencies, comprising a With the values RA=80,000 ohms, Rs=75,000 housing adapted for submersion in the water ohms, RR=21,000 ohms, Co=942 1012 farads, C1=29.1 10l2 farads, the calculated eiliciency of conversion is shown by the dotted curve A of Fig. 8. This represents the efciency of conversion from electrical to total acoustic energy. When using the device to measure pressure, only the energy on one side is useful so that for radiation from one side the conversion efliciency is three decibels lower as shown by the solid curve B of Fig. 8.

Fig. 9 shows an experimentally obtained response-frequency characteristic of the device described hereinabove. The input to the projector was ten watts, the pick-up microphone being located two feet distant in the water from the projector and the microphone amplifier having a gain of 80 decibels. The dotted curve C represents the composite response 0f the projector, microphone and recording system associated therewith. After correction for the system and the microphone response as a function of frequency, the solid curve D was obtained as the projector response-frequency characteristic. The dot-dash line E represents a characteristic in which the response varies by six decibels per medium, including a frame and a pair of diaphragms affixed to and extending across the open portions of said frame so as to provide an enclosed space therebetween, a pair of thin electrically insulating plates each respectively aiiixed to and contacting substantially the entire inner surface of a diiferent one of said diaphragms, a plurality of piezoelectric crystal units connected electrically in parallel with each other and supplied with electrical energy of said band of frequencies, each of said units comprising a plurality of electrically-connected Rochelle salt crystals, said plurality of crystal units being fastened to and arranged between said insulating plates within said space so that the array thereof, collectively, contacts substantially the entire inner surfaces of the insulating plates, thereby applying the mechanical vibrations produced in them in response to the supplied electrical energy through said insulating plates uniformly over the entire area of each of said diaphragms, the outer surfaces of both of said diaphragms contacting directly with and radiating acoustic energy to said medium when said housing is submerged therein.

7 'SQThe device of claim 4,n lwhich each Rochelle salt crystal in each of said crystal units is 45idegree Y cut and said crystal units are separated fromv each other and said frame by dry Rochelle salt crystals to -maintain the humidity 5 10W Within said enclosed space. Y

6. The device of claim 4 in which each Rochelle salt crystal in each crystal unit is 454degree Y cut, said crystal units being assembled symmetrically Within said enclosed space in a plu l0 'ral'ity of rowseach ncomprising thesjanie nuniber of '1,1I1ts,v extending between diierent' portions of the two insulating plates, the asserrilolyl being onercrystal wide in the radiation direction, so that all the individual crystalsvilorate in unison in response to the supplied electrical energy to provide uniform'vibration of al1 parts of each diaphragm through the insulating plates.

WARREN P. MASON 

